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THE 9.5MM PATHÉ PAX
SOUND FILM PATH MODIFICATION
by Grahame Newnham B.Sc.
The Pathé Pax optical sound projector arrived in the UK around 1950. It was a 'budget' UK version of one of the post-war French Pathé Joinville designs. Whilst the version sold in France seems to have had a steel pulley / flywheel and set screw adjustable speed governor; the UK version (in an attempt to get the price down a bit, I guess) had a 'mazak' casting for the pulley / flywheel (which these days is normally bulging or crumbling) and a speed governor set by bending with pliers! It certainly gave a creditable performance on new 9.5mm optical sound prints, but for smoothing of the film between the intermittent and the sound head, a chute was used to 'pinch' the sides of the film (like the early 17.5mm Home Talkie), and in theory at any rate, to keep the tension on it constant as it travelled over the sound drum. In practice, variations in film width, particularly at splices, tended to upset that constancy.
Many users modified this design often using extra 9.5mm rollers in place of the chute. I believe letters had appeared in the UK Amateur Cine World magazine in the 1950s, but in June 1961 an interesting piece appeared in the Centre Sprocket column, showing a design by R.M.('Bob') Bayley from Birmingham including excellent engineering drawings. Basically he made a new assembly that fitted onto the chute bracket.
New roller smoothing device replaces the chute
The new arrangement comprises two grooved brass pulleys (rollers) mounted on 4BA steel shafts fixed to the brass mounting plate. The rotation of each pulley is controlled by a weak compression spring mounted on the shaft between the adjuster nut and the side of the pulley (roller). The groove in the pulley is the width of the film, and is 1/16inch deep. The spring loaded jockey pulley rides in the path of the two grooved pulleys. The tension of the film is effected by the combination of the adjustment of the small compression spring on each grooved pulley shaft and the depth at which the jockey rides between each grooved pulley.
Below is the design of the rollers used, but maybe standard 9.5mm rollers can be obtained from a scrap projector. I have seen a number of Pax machines modified in a similar fashion, with a great improvement in sound steadiness on older film prints.
1. Based on a piece from the 15th June 1961 UK Amateur Cine World magazine Centre Sprocket column.
2. I have used the term 'pulley' as it is used in the original piece, but I think 'roller' would be a better description.
3. The 16mm UK Pax projector was similar, so much the same design applies, but with 16mm rollers of course..
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Last updated: 19 June 2016 ..................... 95gearpat1paxmod.htm .......... ©MMX1V Grahame .L. Newnham